The present invention relates to high performance butterfly valves, and more particularly, to high performance butterfly valves wherein the pivotable disk which is rotated to open and close the valve has a partially beveled outer periphery.
Butterfly valves, in general, are well known and widely employed due to their simplicity of construction and relatively inexpensive cost as compared to more complicated and detailed plug and ball valves. In recent years, the demand has been increased for butterfly valves containing an offset axis of rotation of the disk. In an offset rotation valve, the axis of rotation of the disk is slightly offset from the center of the bore through the valve. Offset valves provide a camming action to the disk when coming both into and out of a sealing arrangement with the valve seats. So that less force is required to open and close the valve.
However, one detraction to the use of offset rotation butterfly valves is extensive contact between the disk and the valve seats which can cause an undue amount of wear on the seats. If a metal or other relatively rigid material is employed as the valve seat, the camming action of an offset valve may wear or damage the seat as the disk is brought into sealing arrangement with the seat. Wear or damage along the sealing surface will eventually lead to leakage of the valve. Accordingly, the effective lifetime of the valve is reduced.
Butterfly valves, including arrangements for reducing the extensive contact between the disk and the valve seats during offset rotation, are known. U.S. Pat. No. 4,058,290 to Nelimarkka and U.S. Pat. No. 4,037,819 to Kindersley both disclose butterfly valves with arrangements for reducing the contact between the disk and the valve seats. Nelimarkka discloses a cylindrical angle-transported disc so that disk appears to be a cross-section of a ball. The end edges are angled at an angle greater than 0.degree. with respect to a line drawn perpendicular to the faces of the disk.
Kindersley, on the other hand, discloses a conical angle transported disk so that the disk appears to be the diagonal cross-section of a cone. Again, the end edges are angled at an angle greater than 0.degree. with respect to a line drawn perpendicular to the disk faces. Both Nelimarkka and Kindersley have the angled ends to allow the disk to slide into position. However, both valves have proven to be less than satisfactory in reducing the contact between the disk and valve seat during rotation of the disk.
Accordingly, the need remains for an improved high performance butterfly valve with reduced contact between the disk and the valve seat during rotation of the disk.